7 Signs of Heat Stroke That Every Cyclist Should Recognize

When the weather finally warms up, there’s no better feeling than ditching your trainer for a long, sunny ride. But once the summer heat reaches sweltering temps, taking things outside can pose some risks.

The two are similar, but have some key differences. Heat exhaustion comes down to a couple of factors: exposure to uncomfortably high temperatures over several days, and a lack of fluids. This can lead to lots of sweating, rapid breathing, and a fast but weak pulse, according to the U.S. National Library of Medicine.

If left ignored and your symptoms get worse, heat exhaustion can actually develop into heat stroke, a deadly illness that occurs when your body temperature soars very quickly, spurring a chain of even more unpleasant symptoms. Here’s everything you need to know about heat stroke and exactly how you can keep yourself safe this summer.

What is heat stroke?

Traditional heat stroke generally comes on gradually and affects very young and elderly people whose bodies have trouble maintaining its core internal temperature. People who don’t have a way of cooling down—say, folks who live in a building without air conditioning—are also at risk of traditional heat stroke. In these instances, the person may not realize they’ve become hot because their body temperature is steadily rising over many hours or days.

Exertional heat stroke is more sudden and occurs in people who are active in high temps. It can affect anyone working out in the heat, but endurance athletes (like cyclists), football players (who sweat it out in stifling equipment), and laborers (like construction workers) face the highest risk.

So in turn, your internal temperature continues to rise—and when it reaches 104 or 105 degrees Fahrenheit, that’s when things start to get really dangerous. When you get that hot, the cells inside of your intestines get damaged, which can leak toxic substances into your blood and cause multiple organs to fail, Pryor says.

What are the most common signs of heat stroke?

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1. High body temperature

If your body temperature hits 103 degrees Fahrenheit or higher, you could be dealing with heat stroke, according to the CDC. If you take someone’s temperature and it’s lower than that—but they still exhibit other heat stroke symptoms or feel that something is wrong—you should still do what you can to cool them down and get medical help, Pryor says.

That’s because thermometers aren’t always accurate. “Someone might have a body temperature of 106, but if you get an oral temperature, they might only be 100 degrees,” he warns. “You might think they’re just a little warm when, in fact, they’re dangerously hot.”

2. A lack of sweat—or an abundance of it

When you spend a long time in extreme heat, the body stops trying to maintain its core internal temperature. So during traditional heat stroke (remember, that’s the kind that comes on gradually), you may actually stop sweating.

However, you’ll probably start sweating like crazy if you’re experiencing exertional heat stroke—it’s a myth that you stop sweating. “I’ll commonly hear people say [they] know it’s not heat stroke because they are still sweating and that’s not true,” Pryor explains. “With exertional heatstroke, many times we see the individual well before they’ve ‘cooked’ themselves and the body is still trying to thermoregulate [maintain its core internal temperature]. If anything, you’re actually going to see the individual sweating profusely.”

3. Confusion or trouble walking

Exertional heat stroke throws your central nervous symptoms out of whack, so a lack of coordination, confusion, aggression, or the inability to walk are huge red flags, says Pryor. “It’s kind of like a concussion where the lights are on, but nobody’s home,” he says. “They can’t answer questions appropriately, and that’s the first [signal] that we see.”

4. A pounding headache

A throbbing headache is common with heat stroke. This symptom is typically due to dehydration, or the overall impact heat stroke has on the central nervous system.

5. Dizziness, nausea, or vomiting

As you continue to sweat, your body will become increasingly dehydrated. The heat will start to affect various organs, all of which can exacerbate any of the symptoms on this list and can lead to dizziness, fainting, nausea, or vomiting.

6. Skin redness

In instances of both traditional and exertional heat stroke, when the body tries to cool itself down, it directs blood flow toward the skin, making it appear red. Your skin may also feel unusually clammy or exceptionally dry, depending on what type of heat stroke you’re experiencing.

7. Elevated heart rate or trouble breathing

Your heart is put under an immense amount of stress when you overheat. Why? It needs to pump harder and faster to make sure your body’s natural cooling systems are working to keep your temperature balanced. This could lead to trouble breathing or hyperventilating.

What should you do if you think someone has heat stroke?

If you think someone is dealing with heat stroke, dial 911—the situation can be life-threatening. The next best thing you can do is rapidly and aggressively cool the person down while you wait for help to arrive. Here are a few measures Pryor says you can take:

Move the person to a cooler place. Get them out of the sun and into the shade or a cool room indoors.

Fill a tub with ice water and have the person soak for 15 to 20 minutes.

If a tub is not available, hose them down with cold water, pour a bottle of water over their body, or take them to a nearby lake or river.

Get them to drink water or a sports drink. This might be difficult if the person is extremely light-headed, confused, and irritable, so you might need to wait until they cool down before they can tolerate fluids.

How to prevent heat stroke

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There are steps you can take to minimize your risk of heat stroke. First, make sure you drink to thirst if you are exercising in the blistering temps. Current guidelines recommend that men get at least two to three liters of water per day, while women should aim for 1.6 to 2.2 liters per day. For most people, this should be enough, says Pryor.

However, if you’ll be doing high-intensity exercise, you should drink to match your sweat loss. Here’s how to figure that out: Weigh yourself naked and then go exercise. Afterward, wipe down the sweat and weigh yourself naked again. That difference in body weight (as long as you didn’t eat anything or go to the bathroom) is primarily going to be due to the amount of fluid you lost from sweat, Pryor says. Convert how many pounds you lost to ounces, and that’s how much water you should drink. So, if you lost one pound of water, next time you workout, make sure you drink at least 16 ounces of water.

Another tip: start slow and let your body acclimate. Even people who are in great shape need to work up to sweating it out in the sun. Pryor recommends decreasing the duration and intensity of your workouts for a couple of weeks. As you continue to exercise outside in the hot weather, progressively work your way back up to your normal workout. This gives your body some time to adapt so you can enjoy the weather safely.

Alisa HrusticAssociate EditorAlisa Hrustic, an associate editor at Prevention, has spent her entire career interviewing top medical experts, interpreting peer-reviewed studies, and reporting on health, nutrition, weight loss, and fitness trends for outlets like Women’s Health and Men’s Health, where she both interned and worked full-time.

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